Long bones are those greatly elongated bones such as the femur or tibia that are found in a human or in an animal. When a long bone is fractured, the surgeon immobilizes the various bone segments relative to one another to promote healing of the fracture. The immobilization or fixation of the segments is accomplished by the use of one or more rigid devices that span the fracture site and are located either external to the body or internally on the bone surface or inside the bone canal.
This invention of a flexible intramedullary fixation device was first proposed and submitted to the National Institutes of Health as a Small Business Innovation Research proposal “Retrograde Femoral Reconstruction Fixation System” on Aug. 14, 1997 and assigned Application Number 1 R43 AR45345-01. A revised application, #1R43 AR45345-01A1 was resubmitted on Apr. 14, 1998. The applications describe a flexible intramedullary nail that is inserted into the medullary canal of a long bone to align and stabilize the fracture by providing proximal and distal locking.
External fixation devices are typically located outside of the body, with the only components that enter the body and bone being metal pins. One such external device is known as a Hoffmann device. Another such device is known as a Brooker frame. Both are characterized by plural pins lodged in each bone segment. The pins are oriented transversely to the bone and exit the body. Frames that are exterior to the body connect the pins together. External devices not only prohibit movement of the bone segments relative to one another, but they also provide longitudinal compressive force on the bone segments, causing the segments to contact one another at the fracture site. Such compressive contact between the bone segments is desirable because it creates a physiological stimulus to unite the bone segments. However, external devices have many problems. External devices are difficult to manipulate to achieve the desired compressive force. Also, once the devices are set in the desired position, they can be inadvertently manipulated. Furthermore, external devices are inconvenient for the patient and present an increased chance of infection along the metal pins that penetrate the skin and underlying tissue.
Internal fixation devices include either cortical plates which are located on the exterior of the bone cortex or intramedullary nails which are located in the bone's intramedullary canal. The cortical plates are implanted surgically in a single operation and usually require an extensive operative procedure and exposure of the bone. Cortical plates, which are fastened to the bone cortex by screws, can apply slight compression to the bone segments. However, cortical plates are applied at the fracture site, carry the risk of infection and excessive blood loss and require extensive surgical exposure. Intramedullary nails are stainless steel or titanium rods that are inserted within the central, medullary canal of the bone, span the fracture site and are locked in place above and below using screws. The nail can be either driven from the proximal end to the distal end (antegrade) or from the distal end to the proximal end (retrograde). Prior art nails include Schneider nails, Kuntscher nails and Ender nails. Schneider nails are longitudinally fluted rods with small teeth on the ends. The teeth allow a trough to be cut as the nail is driven down the canal. Kuntscher nails are hollow rods with longitudinal flutes. Intramedullary nails range in diameter from 9 to 16 millimeters in diameter. Ender nails are flexible rods 2 to 3 millimeters in diameter or diamond shaped rods that may be curved. Intramedullary nails reduce the risk of infection since there is no continued penetration of the skin and are inserted away from the fracture site. Intramedullary nails also prevent inadvertent manipulation. However, prior art intramedullary nails fail to provide compressive force along the length of the bone.
The use of intramedullary nails or rods has become the standard method for the treatment of fractures, malunions and non-unions of long bones, i.e., the femur and tibia in the lower extremities and the humerus, radius and ulna in the upper extremities. The typical surgical procedure for such treatment involves the insertion or implantation of a nail or rod into the intramedullary canal of the subject bones such that the nail spans the fracture(s) and/or non-union or malunion. Interlocking screws are then placed through bores or apertures within the intramedullary nail, interlocking with the nail and extending through the bone on both sides of the treatment site. As such, the bone and/or bone fragments are stabilized and immobilized against rotational and lateral movement in order to allow the bone to properly set and heal, and to prevent displacement of the fracture during the healing process.
Moreover, intramedullary nails have consisted of relatively rigid structures inserted into relatively curved bones such as the femur, tibia, humerus and radius. These fixation rods have relationships between their bending and torsional rigidities that are substantially different from those of the intended intact long bone. This can result in shielding the fracture from the natural loading stresses and inhibiting callus formation. In addition, the intramedullary nails are manufactured in a pre-bent configuration to supposedly to match the curvature of the intended long bone but variation of natural curvature and there is typically a double curvature to the long bone cause a mis-match in curvature. This mis-match in curvature can cause great difficulty for the surgeon to insert the nail down the intramedullary canal or causes the bone to conform the curvature of the nail leading to malreduction or unsatisfactory positioning of the fracture fragments.
Retrograde intramedullary nailing, first described by Harris in 1980, has become common recently. For critical patients with multiple injuries, femoral shaft fractures can be stabilized quickly and efficiently, and bilateral lower extremity injuries can be treated simultaneously in the supine position. Although the absolute indications for the use of retrograde nails are still the subject of some debate, relative indications include morbid obesity, multisystem trauma, ipsilateral floating knee and/or tibia injuries, bilateral femur fractures, ipsilateral acetabulum and/or femoral neck fractures, uncontaminated traumatic knee arthrotomies, through-knee amputations, pelvic ring injuries, pregnancy, gross contamination around the insertion point for antegrade nailing, unstable spine injuries, and multiple fractures. For properly selected cases, limited use of retrograde nailing is recommended by most researchers. Retrograde insertion of a reamed intramedullary titanium nail through an intercondylar approach within the knee joint is used for femoral shaft fractures in most applications. The nail is introduced along an *inserted guide pin and countersunk under the intercondylar notch to preclude the possibility of damage to the patellofemoral joint or other articular structures and resultant late degenerative joint disease. Potential complications associated with retrograde nailing, including knee stiffness or impaired function, quadriceps atrophy, articular or cruciate ligament damage, and septic joint. Researchers have concluded that antegrade and retrograde nailing appear to be comparable as far as union rates and bony fusion latency are concerned.
One of the methods of fixation is fixation with locking retrograde intramedullary nail. It is used in intertrochanteric fractures, FIG. 2. Longer locking retrograde intramedullary nail can be used to fixate complex fractures, combined of distal and middle femoral fractures, or in fractures of the middle and lower parts of the femur, where access with a locking antegrade intramedullary nail is not possible (e.g. in patients with total hip arthroplasty, in non-union proximal femur fractures with implanted osteosynthetic material). The method is very good for fixation of fractures in older patients with a weak bone structure, in cases of pathological factures, and in poly-traumatized patients whose condition allows complete treatment. Locking retrograde intramedullary nail is also used for fixation of corrective supracondylar osteothomy and for fixation of supracondylar fractures in patients with total knee arthroplasty.